High‑index‑faceted and electron density-optimized Ni3S2 in hierarchical NiWO4-Ni3S2@NiO/NF nanofibers for robust alkaline electrocatalytic hydrogen evolution

•{1 2¯ 3} faceted NiWO4-Ni3S2@NiO/NF electrodes with tunable S vacancies were devised.•The facets and S vacancies on Ni3S2 determined the overpotential (η) and TOF in HER.•A η10 of 89 mV and a TOF of 1.5 × 10−3 s−1 were attained on NiWO4-Ni3S2@NiO/NF-3.•DFT calculations revealed the manipulation mechanism of facets and S vacancies.•An overall-water-splitting current density of 10 mA cm−2 at 1.64 V was achieved.